A conventionally known type of fuel cell stack is a solid oxide fuel cell stack (hereinafter, may be referred to merely as a fuel cell stack) which uses a solid oxide as an electrolyte layer.
For example, Patent Document 1 mentioned below describes a known fuel cell assuming the form of a flat plate and having a laminar solid electrolyte formed of a solid oxide having ion conductivity, a laminar cathode provided on one side of the solid electrolyte and contacting with oxidizing gas (e.g., air or oxygen), and a laminar anode provided on the other side of the solid electrolyte and contacting with fuel gas (e.g., hydrogen, methane, or ethanol). Also, there has been developed a fuel cell stack having a structure in which a plurality of the fuel cells are stacked.
In order to favorably perform reaction between the cathode and oxidizing gas and reaction between the anode and fuel gas, the fuel cell stack of this type is usually configured to increase contact areas between the electrodes and the gases. For example, regarding a cathode side, oxidizing gas is introduced toward the cathode from the direction of a side surface of the cathode (i.e., along a direction perpendicular to the thickness direction) so as to supply oxidizing gas into a space between the main surface (the outer surface with respect to the thickness direction) of the cathode and a separator of the cell, thereby supplying oxidizing gas to the cathode.
In another case, for example, in order to establish electrical connection between the cathode and an external device (a device outside the cell), a current collector is disposed in contact with the outer surface of the cathode (the main surface of the cathode). In recent years, in order to ensure electrical communication between the cathode and the current collector, for example, increasing the thickness of the cathode has been proposed (see Patent Document 2 mentioned below).